1. Field
Various embodiments of the present invention relate to an image sensor, and more particularly, to a differential amplifier on the basis of an input common mode voltage sampling, and a dual mode comparator using the same.
2. Description of the Related Art
A differential amplifier of a class-A type is used as a comparator included in an analog-digital converter for performing an analog-digital converting operation to cancel a banding noise, which occurs in a complementary metal-oxide semiconductor (CMOS) image sensor.
In a CMOS image sensor, a differential amplifier for comparing a pixel output voltage, which is received from a pixel, with a ramp voltage (i.e., a reference voltage) is used in a first amplifying stage of a comparator. However, in a case where an output of the first amplifying stage is inputted to one of two input terminals of a second amplifying stage of the comparator (i.e., a single-ended), when a differential amplifier is used as the second amplifying stage, the other terminal of the second amplifying stage receives an input common mode voltage having a predetermined voltage level.
In such case, when the input common mode voltage is provided to a plurality of comparators, e.g., 2500 comparators in a CMOS image sensor having 5 Mega pixel, various coupling may occur between the input common mode voltage and adjacent nodes within each comparator depending on an operation condition of each comparator. Thus, if the comparators operate at different points in time, distortion in an input signal processing may occur while the analog-digital conversion is performed.
To resolve such concern, a conventional circuit performing a self-sampling operation on an input common mode voltage has been employed. In the conventional circuit, since a fixed voltage with a predetermined level is to be sampled, the same power supply voltage may be applied for both of the first amplifying stage and the second amplifying stage. Further, the circuit may not be used at a low voltage due to the operation margin.
Thus, a new technique may be required to address such concerns.